Force a complete cold start

[Peter D]

Hello,

I would like to understand if it is possible to force a completely cold start on my Pixel 8 without factory resetting the phone.

The state I'm trying to get to is all almanac, ephemeris, assist, and prior location data gone.  As if the phone was turned on for the first time.

Is this possible?  Googling seems to suggest that turning location services off and on should be enough, but I've tried this and the results don't seem entirely consistent, so I am unsure as to whether it really achieves a cold start.

My phone is a Pixel 8.

Android 16 (API level 36)

Broadcom BCM4776, HW year 2020.

Thanks in advance for your help.

Regards,

Peter.

[Sean Barbeau]

Hey Peter,

The AGNSS tab "Clear APS" option in GnssLogger or main menu "Clear assist data" in GPSTest should give you a cold start.

Note that this works on Pixels, but there's some phones (IIRC Samsung devices) that this doesn't work on.

Sean

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[Peter D]

Thanks very much Sean!

This is exactly what I needed to find out.  I appreciate your help very much.

Regards,

Peter.

[Peter D]

Hi Sean,

It might be the case that this process doesn't work on the Pixel 8.

I have a Faraday cage with a GNSS simulator transmitting internally.  I have a small number of receivers inside the cage.

I know that the simulator is not using a current almanac or ephemeris data.

When I attempt the process to initiate a cold restart, I watch the Status view of the GPSTest App.  Reasonably quickly I start seeing SVs with the E flag, and then within no more than 2 minutes all the SVs also have the A flag.  It seems too quick.  Despite the signals from many of the individual SVs being reported with C/N0 over 40, and most of the SVs reporting azimuth & elevation, my phone only occasionally reports a fix.
The devices that are left in the Faraday cage generally report fixes quite quickly and with reasonable accuracy, which suggests to me that my phone is holding onto the real world almanac and ephemeris data from outside the cage, despite my attempts to delete it.

There is no apparent difference whether I use "Clear AGPS" in GnssLogger or "Clear Assist Data" in GPSTest.

I'm wondering if the other apps on my phone that are using Location Services are preventing the cold restart?

Regards,

Peter.

On Sunday, 21 September 2025 at 02:45:01 UTC+10 sjba...@gmail.com wrote:

[Peter D]

Hi Sean,

I've tried a couple of tweaks, and finally I had success after I turned "Location for Work Profile" off and and also "Location Services" off, and then pressed "Clear Assist Data" in GPSTest.  When I turned Location Services back on, the SVs turned up in the Status view without any 'A' flag (but the 'E' flag turned up quickly), and my Pixel got a location fix that agreed with the simulator, and is holding it solidly.

Regards,

Peter.

[Sean Barbeau]

Interesting! Thanks for sharing the trick with "Location for Work Profile", maybe that was blocking the clearing of assist data.

Turning "Airplane mode" on before deleting the assist data is also a good idea in general, although I assume that the Faraday cage should be blocking cell and Wi-Fi signals anyway.

Sean